The invention relates to restoring torque generating devices for generating a restoring torque acting on a steering handle of a vehicle.
Such restoring torque generating devices in particular are used in steer-by-wire steering systems, in order to generate a restoring torque which counteracts a torque generated by a vehicle operator via the steering handle. The generation of such restoring torque is required, as in steer-by-wire steering systems the steering handle and the vehicle wheels are mechanically decoupled from each other and a desired steering angle entered by the vehicle operator via the steering handle is exclusively electrically transmitted to positioning units/actuators for steering the vehicle wheels, so that forces acting on the wheels during a steering movement are not passed on to the steering handle.
To nevertheless provide the driver with a driving feel similar to a conventional steering system, e.g. electronically actuated actuators (for example in the form of an electric motor) are used for generating a restoring torque. In addition, a purely mechanical generation of a restoring torque can be effected. In particular, there is used a combination of an electric actuator and a mechanical restoring torque generating device, wherein for the case of a defect (for example in the case of a failure of the vehicle electronics or in case the electric actuator no longer is actuatable for other reasons) the mechanical restoring torque generating device provides a fallback level.
Another aspect for the use of additional mechanical restoring torque generating devices is the relief of the electronically actuated actuator, so that the operation of the actuator can be effected with lower power.
A mechanical restoring torque generating device is described for example in DE 101 59 330 A1. There is disclosed a reaction torque simulator which for generating a restoring torque comprises two spiral springs which are loaded or unloaded depending on the direction of rotation of a steering shaft. Tensioning of the spiral springs is effected via a driver, wherein the construction however merely allows tensioning of the spring over an angular range of less than 360°. For this reason a transmission is located between the spiral springs and the steering shaft, via which a rotation of the steering shaft is transmitted to the driver.
The integration of a transmission in the steering wheel region however requires measures for damping noises and vibrations. Another disadvantage of the transmission can consist in that (as seen from the spiral springs) a small angle of rotation must be translated into a higher angle of rotation at the steering handle. As the transmitted angle of rotation is inversely proportional to the rotational speed, this means that for generating high restoring torques the spiral springs must be dimensioned correspondingly; in particular, the spiral springs must have a correspondingly high spring constant.